The digital representation of waveforms is a technology that is central to various sectors of industry where the detection of periodic and non-periodic waveforms can be critical to determining whether an erratic heartbeat, electrical short circuit, or some other problem exists. A digital representation must clearly and accurately represent the analog source of a waveform, but at the same time be able to accomplish such things as, compressing the incoming data into some manageable size, and maintain the integrity of the incoming data (i.e., making sure that the digital representation has enough fidelity to the original signal to be useful). Of additional import is the ability to have a digital representation that can consistently allow one to identify the presence and location of certain wave features, and/or that lends itself to certain types of automated analyses.
High-fidelity digital representations are problematic for a number of reasons. First, they require relatively large amounts of space within which to store the digitized data. Put another way, the higher the fidelity of the digitized data, the larger the amount of storage needed. Another problem with high-fidelity digital representations is that they can result in large amounts of digital data that has little or no import in terms of conveying meaning. For example, a periodic wave signal that merely repeats the same waveform does not convey much meaning to the person analyzing the waveform, and may in fact just take up storage space with unremarkable data. An additional problem is the repeated sampling, over sampling of such high-fidelity data even though it is otherwise unremarkable. Such over sampling results in wasted processing bandwidth (i.e., processor cycles, and/or power) as well as data bandwidth (data storage space and/or transmission bandwidth).
U.S. Pat. No. 8,086,304 issued on Dec. 27, 2011, with the title “Physiologic signal processing to determine a cardiac condition,” and is incorporated herein by reference in its entirety. U.S. Pat. No. 8,086,304 describes, that in a method for determining a cardiac condition, a sensed physiologic signal for a period of time including multiple cardiac cycles is received. A plurality of harmonics of the received physiologic signal is extracted based on a reference frequency, wherein the harmonics correspond to a plurality of alternans frequencies. Amplitudes of at least some of the extracted harmonics are determined, and are used to determine an alternans indicator value.
What is needed is a method and structure that efficiently and accurately captures the underlying waveform, with little or no degradation of the value and meaning of that waveform data. In particular, what is needed is a method and apparatus that tracks and records the properties of a particular frequency component of a complex waveform.